ITS3 sensor prototype characterisation for the second upgrade of ALICE Inner Tracking System

ALICE (A Large Ion Collider Experiment) is one of the 4 main experiments at CERN Large Hadron Collider (LHC), aiming to investigate Quantum Chromo-Dynamics (QCD) at different momentum scales through the study of proton-proton and heavy ion high-energy collisions. Within the theory of the Standard Model, the field of QCD focuses on the strong interaction, that binds quarks and hadrons. At the moment, ALICE is undergoing its third measurement run, Run~3 (2022 -- present). The main goal of the ALICE experiment is to reproduce the conditions for a state of matter consisting of strongly interacting free partons, i.e. the Quark-Gluon Plasma (QGP), by colliding proton and heavy ions at very high center-of-mass energies of the TeV scale. Currently, energies can go as up as $\sqrt{s} = 13.6$~TeV for proton-proton (pp) collisions, and $\sqrt{s_{\mathrm{NN}}} = 5.36$~TeV for Pb--Pb. This allows to investigate the properties of QGP, by detecting and reconstructing the products of its evolution: each kind of outgoing particles, from photons to charmed and beauty hadrons, can serve as a probe for different characteristics of QGP, e.g. its temperature, hydrodynamic properties, or hadronisation process. For this purpose, a variety of different detectors are employed to track and identify the final products of proton and heavy ion collisions in ALICE, most prominently charged hadrons and photons. In the following, an outline of heavy ion collision processes will be first given. We will then move on to a short description of the ALICE detector and its specific sub-detectors. After that, we will focus more specifically on the state of the art of ALICE Inner Tracking System (ITS2) and its upgrade to ITS3, scheduled for the upcoming Long Shutdown~3 (LS3, 2026-2029). The new ITS3 will feature bent, stitched large-scale sensors as tracking layers, and is expected to further improve the ITS tracking and vertexing capabilities. The main focus of this thesis work will be the results of characterisation tests performed on small-scale analogue and stitched digital test devices, within the framework of the R\&D for the ITS3~upgrade. Furthermore, to give a hint of the results already attainable with the present ALICE Run~3 data, some early analysis results of strange K$^{*}(892)^{\pm}$ resonance yields will be presented.